[Cob] earthen plaster on drywall

[Shawn King]

Hi Anna, I posted a reply a few days ago but I believe I did two things
wrong - I hit reply to you alone, and I also included a link in the post.
I am reposting with both conditions corrected. My wife Melissa and I
applied earthen plasters over unpainted as well as glossy- and
matte-painted sheetrock successfully. Applications were in the kitchen and
bathroom, so the approach seems to work quite well in rooms where water
vapor is produced in concentrated amounts. You need a thin adhesion coat
first followed by whatever earthen plaster you want. We tried adhesion
coats based on wheat and rice paste and sand and found they led to staining
of the final plaster, so we now avoid this method. We now use what we call
"schmeer" which is just clay rich soil mixed with water and coarse sand to
make a sticky, gritty paste the consistency of yogurt. We take this and
smear it onto the sheetrock in a circular motion with pressure to form a
thin layer, just enough to cover the sheetrock, and let it dry.  Just
before applying an earthen plaster, we re-wet the schmeer so that it is
nice and damp, but not so much that it starts to wash back off the
sheetrock.  The earthen plasters we like are just our somewhat silty
subsoil (soaked and screened through 1/8th inch screen), water, screened
horse manure (through 1/4 inch screen), and screened sand, maybe 2:4:1 or
whatever gets us to a consistency like fluffy tuna salad when mixed wet.
If we want a plaster color other than the natural result of this mix, we
wait for the plaster to dry completely and then paint over it with
lime-buttermilk paint tinted with masons or potters stains. I find earthen
plasters eat a lot of pigment, wasteful and expensive, so I prefer paint
for final effects. Hope this helps.  Best, Shawn

On Wed, Feb 22, 2017 at 12:51 PM, <avjyoung at shaw.ca> wrote:

> We are having to drywall our cob/strawbale house over the framed areas,
> rather than time-expensive lathe and plaster as our old house is falling
> apart and very close to uninhabitable. What, if any, earthen plaster can we
> put over the drywall to get the different surfaces looking more similar,
> and avoid using drywall mud and toxic paint?
>
> Thoughts and comments very welcome!
>
> Anna
> cob-strawbale hybrid in Victoria, BC.
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